1. Field of Invention
Deposits of tar sand occur at many localities throughout the world, however, the Athabasca Tar Sand deposit of northern Alberta in Canada represents an estimated reserve which exceeds the combined proven oil reserves of the rest of the world.
The tar sand originated from a deposit of ordinary oil that once lay buried beneath an ancient body of water, for example, a sea. The land area at the bottom of the sea rose and the water disappeared. The oil migrated upward into the still-wet sea floor because the surface pressure was insufficient to hold the oil down. Because the sea floor was still wet when the oil migrated upward, a film of water and seashore clays, including metals, separated each grain of sand from the oil. The oil covered the sand particles, trapping the thin film of water between the oil and sand particles. The oil in the tar sand is no longer oil as we know it because the lighter hydrocarbons evaporated long ago due to the action of sunlight on the original oil. All that is left of the original oil are the heavy, carbon-rich hydrocarbons, plus sulfur and other impurities, for example, various metals, sand and water. The tar-like oil thus defined is in actuality a form of bitumen. Since the original upward migration of the oil through the sea bed, the eons have dumped boulders, gravel, sand, clay and the like atop the tar sand. However, to mine and process the tar sand using conventional methods costs at least three times more than it costs to drill and pump up natural crude. Thus, because of the world's dwindling supply of petroleum and energy-related resources, it is highly desirable to extract oil from tar sand efficiently and economically. In accordance with the process defined and claimed herein, substantially metal-free tar sand bitumen is recovered from tar sand using a halogenated aliphatic solvent in combination with an unsaturated halogenated compound or an oxygenated compound.
With the developing energy shortage, the search for a workable and economically feasible process for extracting oil in the form of bitumen from tar and oil sand has intensified in recent years. Deposits of oil and tar sand occur at many localities throughout the world and represent a potentially large source of oil, however, as to today a workable and economically feasible process for extracting bitumen from these tar sands has not been disclosed.
Many processes for tar-oil sand development have been proposed over the past few years. The processes include direct combustion, solvent extraction, water flotation and many variations of these processes to extract the oil in the form of bitumen. However, the extraction of bitumen from tar sands utilizing past processes has several disadvantages, especially from an economic point of view. One disadvantage of the processes used in the past is a low recovery rate for the bitumen. For example, in a water flotation process only about 50 to about 70 percent of the bitumen is recovered from the tar sand.
Another disadvantage in the case of a solvent extraction process of bitumen from tar sand is that most solvents used in the past have a very strong affinity for the sand, and a significant percentage of the solvent is lost in the extraction and separation step of the process.
Both of the processes above additionally extract undesirable components from the sand particles, for example, metals which contaminate various catalyst systems in a process to upgrade the bitumen to an oil product.
The tar sand herein is characterized by individual grains of sand surrounded by thin films of water which contain sand fines, minerals and metallic contaminants. The thin films of water are further encased by bitumen, with the bitumen partially filling the voids between the individual grains of sand, forming a connecting link in the form of a bitumen bridge. The bitumen contains most of the organometallic compounds which create problems when the bitumen is further processed over typical hydrotreating catalysts which are readily deactivated or posioned by nickel and vanadium. Past attempts to extract bitumen from tar sands resulted in an alteration of the above-described physical configuration and in some oil-wetting of solids; which additionally resulted in oil-rich sludges and solids stabilized emulsions. These sludges and emulsions result in contamination of the bitumen or oil phase with solids and water. Thus, it is very desirable to extract the bitumen from tar sand without rupturing the connate-water envelope containing contaminants, including metals, which surround the individual sand particles.
2. Description of the Prior Art
Several methods have been proposed in the past to extract tar sand bitumen so that it could be processed into oil. For example, Dr. Karl A. Clark, a government scientist, worked out a process in the late 1940's known as the Clark process. The method includes stripping the overburden from the tar sand, mining the tar sand, and extracting the bitumen from the sand using steam and caustic soda. The bitumen is skimmed from the surface of the mixture. The method collects virtually all of the bitumen, however, the bitumen contains about 35 percent water and minerals, including metals.
Another process for recovering bitumen from tar sand is set forth in U.S. Pat. No. 4,017,377, entitled, "Process and Fluid Media for Treatment of Tar Sands to Recover Oil", issued to Fairbanks, Jr., et al, on Apr. 12, 1977. The reference discloses a process, structure, and aqueous bath for recovering oil from tar sand. In particular, the process teaches the steps of contacting the tar sand with a diluent, for example, gasoline and/or naphtha, to reduce the internal fluid friction or viscosity of the oil layers surrounding each sand particle, and then contacting the mixture with an aqueous bath having a slightly raised specific gravity and a wetting agent. The oil is then recovered using conventional methods.
Another method and apparatus for separating hydrocarbonaceous substances from mineral solids is set forth in U.S. Pat. No. 3,941,679, entitled, "Separation of Hydrocarbonaceous Substances from Mineral Solids", issued to Smith et al, on Mar. 2, 1976. In particular, a solvent extraction technique is employed wherein trichlorofluoromethane is used as the primary extraction solvent. The reference is directed to a process for extracting bitumen from both tar sand and shale.
U.S. Pat. No. 4,046,668, entitled "Double Solvent Extraction of Organic Constituents From Tar Sands", issued to Farcasin et al, on Sept. 6, 1977, discloses a process for recovering hydrocarbons from tar sands using a two-solvent system consisting of a naphtha/methanol mixture which separates the organic matter into three phases. It is to be noted that none of the above references teach a process for recovery of relatively metal-free bitumen from tar sand using a two-solvent system comprising a halogenated aliphatic solvent in combination with a second solvent selected from an unsaturated halogenated compound or an oxygenated compound.